Modulating device for electric telegraph systems



Dec. 15,. 1931. J.'.C. B URKHOLDE R 1,336,441

MODULATING' DEVICE FOR ELECTRIC TELEGRAPH SYSTEMS Filed Aug. 20, 1930 J c. au/iw/mzazw,

' Patented Dec. 15, 1931 UNITED STATES PATENT OFFICE JOHN CHARLES BURKHOLDER, OF TORONTO, ONTARIO, CANADA, ASSIGNOR TO GANADIAN NATIONAL RAILWAY COMPANY, OF MONTREAL, CANADA, A CORPORA- TION OF CANADA MODULATING DEVICE FOR ELECTRIC TELEGRAPH SYSTEMS Application filed. August 20, 1930. Serial No. 476,661.

My invention relates to improvements in modulating devices for alternating current electric telegraph systems, and the object of the invention is to produce the interruption on the output side of the amplifier tube so as not to affect the frequency of amplitude of the oscillations generated by the oscillator tube and also in half duplex operation to dispense with a second relay and provide a break feature, and it consists essentially of the arrangement and construction of parts as hereinafter more particularly explained.

Fig. 1 is a diagrammatic view showing the arrangement of my modulating device.

Fig. 2 is a similar view showing its application to a duplex operation.

In the'drawings like letters of reference indicate corresponding parts in the different views.

1 is a circuit connection leading from a ositive to a negative source, such circuit bemg broken at 2 for the operating key 3. Interposed in the circuit is a sounder 4 and relay 5. 6 is a marking contact of the telegraph system, 7 the spacing contact connected respectively to positive and negative source. 8 is an armature engaging alternately with the contacts 6 and 7 influenced by the relay 5. 9 and 10 are resistance windings connected in series by the winding 9 being connected by a wire 11 to the armature 8. 12 is a wire connected to the outer end of the resistance winding 10 and energized from a positive source. 13 indicates an amplifier tube provided with a plate terminal 14 which is connected by a wire 15 to the series connection between the resistance windings 9 and 10.

16 indicates the output circuit the circuit wires 16 being provided with transformer windings whereby current is induced in the output circuit in the usual manner.

When the telegraph key 3 is closed and the armature 8 of the relay lies over against the marking contact 6 the same positive potential is placed at the ends of the resistance windings 9 and 10. Since the plate 14 of the amplifier is connected to the point 15 common to the windings 9 and 10 the positive potential is applied to the plate of the vacuum tube through the windings 9 and 10 connected in parallel and the amplifier functions to transmitcurrent. When the key 3 is in the open position and the armature 8 lies over against the spacing contact 7 vthe negative potential isapplied at the end of the resistance 9. The point 15 common to the resist ances 9 and 10 is then at a potential depending on the values of the windings 9 and 10. Any values of 9 and 10 may be used which will provide a potential at the plate of the amplifier tube anywhere between alow positive value, suffiicently low as, not to actuate the receiving device, and any negative value as high as the voltage connectedto the spacing contact 7 of the relay 5.

During the time of travel of the armature of the relay a positive potential almost as high as when the armature was against the marking contact 6 will be applied to the plate of the amplifier tube. The cause of the small decrease in potential is that the voltage drop across the winding 10 will be greater now as all the current drawn by the vacuum tube will come through the winding 10 as one end of the winding 9 is free. Thus the sending current will be transmitted during the time of travel of the armature and while the armature is against the marking contact 6. This will give the signal a marking bias which is a desirable feature for practical purposes.

It will thus be seen that the interruptions in this method of modulation are made on he output side of the amplifier tube and thus do not affect the frequency or amplitude of the oscillations generated by the oscillator tube. In the common method of modulation the grid of the amplifier tube is grounded through a condenser. This changes the impedance of the oscillator output circuit and thus the amplitude of oscillations and causes an appreciable shift in frequency.

Also my arrangement does not require a second relay to provide a break feature for half duplex operation in a telegraph system, as illustrated in Fig. 2. When the operator at the distant station is sending signals to the local station and the local operator wishes to interrupt the message, he opens the key 3* in the circuit 1", the armature of the sending relay then moves to the spacing contact 7". Taking the instant when the armature of the receiving relay at the local station is against the marking contact 6 there will be then a negative potential applied to the end of the resistance winding 9 thus sending a spacing signal. This moves the armature of the receiving relay at the distant station to the spacing contact and thus places a positive potential on the end of the sending loop 60,

70. Since there is now the same potential on both ends of the distant operators loop he cannot operate his sounder and thus he knows :Ehat the local operator wishes to interrupt What I claim as my invention is:

In a modulating device for electric telegraphs, the combination with a circuit relay, relay armature, a marking contact coacting with the armature and positively energized, a spacing contact also coacting with the armature and negatively energized, and the plate terminal of an amplifying tube, of a pair of resistances connected in series the outer end of one resistance being connected to a positive source and the outer end of the other resistance to the armature of the sending relay, a wire extending between the connected ends of the resistance and the plate terminal, and an output circuit electrically coupled to said wire.

JOHN CHARLES BURKHOLDER. 

